Ion implantation is a standard technique for introducing conductivity-altering impurities into semiconductor wafers. A desired impurity material may be ionized in an ion source, the ions may be accelerated to form an ion beam of prescribed energy, and the ion beam may be directed at a front surface of the wafer. The energetic ions in the beam penetrate into the bulk of the semiconductor material and are embedded into the crystalline lattice of the semiconductor material. The ion beam may be distributed over the wafer area by beam scanning, by wafer movement, or by a combination of beam scanning and wafer movement.
Differing kinetic energy may be imparted to the ions of the ion beam. The imparted energy, as well as other factors such as the mass of the implanting ions, may affect the implanted depth of the ions into the semiconductor wafer. In general, a lower energy would result in a shallower implant depth and a higher energy would result in a deeper implant depth with all other parameters equal.
Different ion implantation systems may utilize one or more of several methods to impart kinetic energy to the ions of the ion beam. One method of imparting energy to the ions is straight DC acceleration in which the ions are accelerated by passing them through a DC potential difference. The larger the potential difference the more energy is imparted. A mass analyzer may then receive the ion beam and may removed undesired species from the ion beam. Another magnet may collimate the beam and direct it at a wafer. Acceleration accomplished before the mass analyzer such as straight DC acceleration may be referred to as pre-acceleration, while further acceleration after or downstream from the mass analyzer may be referred to as post-acceleration. As used herein, “upstream” and “downstream” are referenced in the direction of ion beam transport.
Straight DC acceleration may utilize one or more power supplies to provide the DC potential. This may include an extraction power supply coupled to the ion source that may provide up to about 70 kilovolts (kV) in one conventional system. The ion source may be at least partially disposed in a cavity defined by a terminal structure. The terminal structure may sometimes be referred to in the art as a “terminal” or “high voltage terminal.” The terminal structure may be energized to 200 kV by a separate acceleration power supply. The combination of 70 kV and 200 kV from the extraction and acceleration power supplies respectively may provide up to 270 kiloelectronvolts (keV) of energy for singly charged ions, 540 keV for doubly charge ions, and 810 keV for triply charged ions.
This 810 keV energy is suitable for many applications but may not provide enough energy for other applications. For example, some memory semiconductors such as Flash memories require higher energy ion implantation systems to create particularly deep well structures. Hence, other high-energy conventional ion implantation systems may be configured to provide energy of 1 megaelectronvolt (MeV) and greater. Such high-energy conventional ion implantation systems may utilize an accelerator downstream from the mass analyzer. The accelerator downstream from the mass analyzer may be a DC tandem-accelerator or a RF linear accelerator as are known in the art. Although effective for providing high energy, the DC tandem-accelerator and the RF linear accelerator may suffer from inefficiencies in that less than about 50% of the mass analyzed ions from the mass analyzer may be available for implantation in the semiconductor wafer.
The ion implantation system may also include an enclosure to protect components and sub-systems of the ion implantation system and to protect personnel from high voltage dangers when the ion implantation system is operating. It is desirable to limit the size of the enclosure or “footprint” in order to save space in a manufacturing facility where space is costly. It is also desirable to make transportation of components and sub-systems less cumbersome. Most conventional straight DC acceleration methods used in volume manufacturing of semiconductors have limited the voltage of the terminal structure to 200 kV since only air is used to insulate the terminal structure from the enclosure and footprint constraints limit the distance of the enclosure from the terminal structure.
Accordingly, it would be desirable to provide an insulator system for the terminal structure of the ion implantation system. It would also be desirable to energize the terminal structure to high voltages with a reasonably sized enclosure footprint.